Ion beam deflector

ABSTRACT

ELECTRICALLY ORIENTING THE THRUST VECTOR OF AN ELECTROSTATIC ION THRUSTOR HAVING A GLASS-COATED GRID SYSTEM. HIGHLY NEGATIVE POTENTIALS ARE APPLIED TO CONDUCTORS THAT ARE MOUNTED IN PAIRS AND ARRANGED IN ARRAYS TO FORM THE GRID. THESE ELECTRICAL POTENTIALS ARE INDEPENDENTLY VARIED IN EACH ARRAY TO OBTAIN THE DESIRED AMOUNT OF ION BEAM VECTORING.

Jam 5, 1971' A, 'BAN ET AL 3,552,125 I I'ON BEAM DEFLECTOR Filed June 6, 1969 FIG. 3

mvzmoas BRUCE A. BANKS HAROLD R. KAUFMAN Q 2% ATTORNEYS United States Patent Ofi ice 3,552,125 ION BEAM DEFLECTOR Bruce A. Banks, Olmsted Township, and Harold R. Kaufman, Berea, Ohio, assignors to the United States of America as represented by the Administrator of the National Aeronautics and Space Administration Filed June 6, 1969, Ser. No. 830,978 Int. Cl. F03h 5/00 U.S. Cl. 60-202 Claims ABSTRACT OF THE DISCLOSURE Electrically orienting the thrust vector of an electrostatic ion thrustor having a glass-coated grid system. Highly negative potentials are applied to conductors that are mounted in pairs and arranged in arrays to form the grid. These electrical potentials are independently varied in each array to obtain the desired amount of ion beam vecton'ng.

ORIGIN OF THE INVENTION The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention is concerned with providing an electrostatic ion thrustor with a single grid accelerator system having a capability of electrically orienting the thrust vector. The invention is particularly concerned with such a system to enable a single thrustor to apply yaw, pitch and roll forces or torques on a spacecraft.

Various devices have been proposed for the thrust vectoring of ion thrustors. These devices have employed conventional double grid systems using mechanical structu'res to displace the accelerator grid relative to the screen grid. This type of mechanical thrust vectoring has the disadvantage of questionable reliability of the moving mechanisms. Also a small displacement of the accelerator grid with respect to the screen grid produces a large deflection of the ion beam. Thus there must be very little error or drift in the amount of grid displacement con trolled by the moving mechanisms. This requires that the moving parts remain moving and repeatable without degradation over lengthy periods of time in space. The moving mechanisms, together with their support mechanical and electrical equipment, also add unwanted mass to the thrustor or spacecraft.

Electrostatic and magnetic deflections of the exhaust ion beam have also been proposed for thrust vectoring. Both types require very high voltages or currents to obtain any significant beam vectoring. This increases both the power conditioning mass and the consumption of spacecraft power.

SUMMARY OF THE INVENTION These problems have been solved by the thrust vectoring system of the present invention. A pair of glass-coated conductors make up each bar of a single grid. The ion beam is deflected by selectively varying the potentials on the conductors.

OBJECTS THE INVENTION It is, therefore, an object of the present invention to provide an electrostatic ion thrustor with an electrically controlled thrust vectoring system having no moving parts.

Another object of the invention is to provide an im- 3,552,125 Patented Jan. 5, 1971 DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an isometric view with parts broken away of a portion of an ion thrustor having a thrust vectoring system constructed in accordance with the present invention;

FIG. 2 is an enlarged elevation view of the grid system on the ion thrustor shown in FIG. 1; and

FIG. 3 is an enlarged sectional view taken along the line 3--3 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT A typical electron bombardment ion thrustor utilizes mercury vapor as a propellant. This vapor is fed into an ionization chamber where it is then bombarded by electrons emitted from a cathode. The path length traveled by electrons going from this cathode to an anode is greatly increased by an axial magnetic field to cause more ionization by electron bombardment. Such an electron bombardment ion thrustor is described in US. Pat. No. 3,156,090.

The ion thrustor may utilize a single grid accelerator system of the type described in copending US. application Ser. No. 758,390 which was filed Sept. 9, 1968. A double grid system having both a screen grid and an accelerator grid may also be used. The screen grid serves to contain the discharge plasma while forming the necessary ion optics to prevent direct impingement of the accelerated ions onto the accelerator grid. Ions in the near vicinity of the screen grid have a high probability of being accelerated through the openings in the grids because of the high electric fields. Thrust is produced as the ions accelerate through the grid system.

Referring now to the drawing, an ion thrustor shown in FIG. 1 has an ionization chamber 10 for containing a propellant that has been ionized. By way of example, this propellant may be mercury that is ionized by electron bombardment as described in the aforementioned US. Pat. No. 3,156,090.

The ion thrustor further includes an accelerator system 12 constructed in accordance with the present invention for accelerating propellant ions away from the chamber 10. The accelerator system 12 includes a single grid 14 of an electrically conducting material that is connected to a source of electric power to impress a potentialon the grid elements. This potential is highly negative relative to the ionization chamber 10.

This single grid accelerator system 12 provides acceptable thrustor performance at low specific impulses because of its efficient ion extraction capability as compared to that of a double grid system. A low specific impulse is necessary to maximize the payload with the high specific mass of solar-cell power sources.

An insulator 16 having an annular configuration extends about the periphery of the ionization chamber 10. The insulator 16 serves to electrically isolate the single grid 14 from the metal housing forming the ionization chamber 10.

The single grid accelerator system constructed in accordance with the present invention is shown in greater detail in FIG. 2. The grid 14 has spaced parallel elements in the form of bars 18 arranged in four separate arrays 20, 22, 24, and 26. All of the bars 18 in each array are parallel to each other and are parallel to the bars in the diametrically opposed array. Likewise all the bars in each array are perpendicular to the bars in the adjacent arrays. By way of example, the bars 18 in the array 20 are parallel to the bars in the array 24. The bars in the array 20 are perpendicular to the bars in the arrays 22 and 26.

Each bar 18 includes a pair of spaced electrical conductors 28 and 30 that are substantially parallel. An electrical insulator 32 covers the surfaces of the conductors 28 and 30 which face the ion chamber 10. This insulator 32 may be glass as described in copending U.S. application Ser. No. 758,390. The insulator 32 protects the upstream surfaces of the conductors 28 and 30 from erosion and maintains these conductors in their parallel relationship.

All of the conductors 28 in the arrays 20 and 24 are connected to a common bus bar 36. Likewise the conductors 28 in the arrays 22 and 26 are connected to a common bus bar 34. The bus bars 34 and 36 extend diametrically across the grid 14 at right angles to each other, and the bars are joined at the center.

A power source 38 is connected to the bus bars 34 and 36. This power source 38 may be in the form of a battery or interconnected solar cells. All of the conductors 28 will have the same potential V as the power source 38. The potential V is the accelerator potential.

All the conductors 30 in the array 20 are connected to a curved bus bar 40 that extends along a peripheral arc of the grid 14. The curved bus bar 40 is connected to a power source 42 such as a battery or a group of solar cells. All of the conductors 30 in the array 20 will have the same potential as the power source 42.

The remaining three arrays 22, 24, and 26 are similar to the array 20. More particularly, the conductors 30 in the arrays 22, 24, and 26 are connected to curved peripheral bus bars 44, 46, and 48, respectively, as shown in FIG. 2. These bus bars are, in turn, connected to their separate power sources 50, 52, and 54, respectively.

Each array 20, 22, 24, and 26 has the capability of controlling the orientation of the thrust vector in a plane perpendicular to the bars 18 in the array. Inasmuch as the entire grid 14 is composed of four separate arrays, yaw, pitch, and roll forces can be produced by the proper application of various electric potentials to each of the four arrays.

Table I illustrates various types of thrust vectoring capabilities for an accelerator potential V and two baising potentials.

The ion beam deflections listed in Table I indicate the direction of deflection of the ions as viewed from upstream of the grid and looking downstream.

V V V and V are the electric potentials applied to the quadrants 20, 22, 24, and 26 respectively of the thrust vectoring grid 14. These potentials can be a biasing potential V the accelerating potential V or another biasing potential V depending on the desired orientation of the thrust vector. Also V is less than 0. V is less than V and V is less than V For example: V =2O0 volts, V =-300 volts, V =400 volts.

Counter-clockwise roll V While a preferred embodiment of the invention has been shown and described it will be appreciated that various structural modifications may be made to the accelerator system without departing from the spirit of the invention or the scope of the subjoined claims. For example, other multidirectional thrust vectoring arrangements, such as glass coated double elements arranged in a pattern of radial slots and grid elements, may be constructed. The insulating coating need not be glass, and the electrical conductors need not be a metal. Any two materials in which one is electrically conducting and the other is electrically insulating can be used if they are compatible with each other and do not degrade during operation of the grid.

What is claimed is:

1. In an ion thrustor having a chamber for containing an ionized propellant and an accelerator system for accelerating propellant ions to form an ion beam, the improvement comprising a plurality of spaced conductors forming a grid in the accelerator system,

means for applying an accelerating potential to said grid, said potential being highly negative with respect to said propellant ions,

means for selectively varying the potential on a portion of said conductors whereby the ion beam is deflected.

2. Apparatus as claimed in claim 1 wherein the surfaces of said conductors facing the chamber are covered with an electrically insulating material.

3. Apparatus as claimed in claim 2 wherein the surfaces are coated with glass.

4. Apparatus as claimed in claim 2 wherein the spaced conductors are mounted in pairs, each of said pairs being coated with insulating material thereby forming a single bar in said grid.

5. Apparatus as claimed in claim 4 wherein each of the conductors in a bar is substantially parallel with the mat ing conductor, and

means for connecting said conductors to separate power sources.

6. Apparatus as claimed in claim 5 including means for connecting one of said conductors in each pair to one power source so that all of said one conductors have the same potential.

7. Apparatus as claimed in claim 6 including means for connecting the other of said conductors in each pair to another power source having a potential that is selectively variable with respect to said one power source.

8. Apparatus as claimed in claim 7 wherein said bars are arranged in a plurality of arrays, each of said bars in said arrays being substantially parallel to the remainder of the bars in that array and substantially perpendicular to bars in adjacent arrays.

9. Apparatus as claimed in claim 8 including a separate source of electrical power for said other of said conductors in each bar in each of said arrays.

10. Apparatus as claimed in claim 9 including a common bus bar connected to each of said one of said conductors in each bar.

References Cited UNITED STATES PATENTS 2,763,125 9/1956 Kadosch ct al. 60230 3,071,154 1/1963 Cargill et al. 60230 Re 26,177 3/1967 Deutsch 60230X CARLTON R. CROYLE, Primary Examiner U.S. Cl. X.R. 60-230; 31363 

